The issue of reliability and durability, in terms of failure rate and life span is one of the most important factors involved in the development of electronic equipment. There is a continuously growing need in the electronic industry for efficient tools for optimizing hardware design, in terms of reliability and durability.
Almost any mechanical or electronic equipment is subjected to varying environmental conditions, such as random vibrations, shakes, dynamic shocks, temperature variations, etc. Such varied conditions may lead to functional failures of the equipment. The designer, manufacturer, supplier and customer strive to avoid such failures for obvious reasons.
For the purpose of determining the durability and reliability of equipment, and in order to forecast and eliminate future failures, various tests of the equipment (also referred herein as “product”) are conventionally performed during the design and manufacturing cycles. These tests may apply a variety of dynamic and thermal loads on the tested equipment, such as random vibrations, dynamic shocks, etc., in order to identify vulnerable components that may fail.
One important and most accepted reliability test is known in the art as the Highly Accelerated Life Testing (HALT). The HALT test simulates and stimulates complex aspects of fatigue by means of applying random stresses in the form of random vibrations and varying temperature conditions. The stresses which are applied on the equipment during a HALT test typically exceed the most extreme expected field conditions, and are intended to reveal design vulnerabilities within a short period of time and before shipment of the product to the customer. While the traditional pass/fail testing approach does not always provide an adequate reliability safety margin, HALT provides a different approach: its philosophy is to enforce failure, not to pass a test.
The use of a HALT test effectively increases the operation margin of the product, creating a wider gap between the specified limits and the actual operational limits. The HALT test is performed in a chamber which applies vibration and thermal loads. Vibrations are the basis of most HALT procedures. The vibration approach which is used by HALT is special. Unlike traditional vibration testing techniques which use a single axis acceleration or excitation at a given time, the HALT exposes the product, which is mounted on a chamber table, to random vibrations in six degrees of freedom simultaneously, i.e., three translational directions and three rotational directions all at the same time. In addition to vibrations, some of the HALT test stages may apply other loading procedures such as hot-cold thermal transitions. As said, the purpose of HALT is to explore potential design weaknesses before introducing the product into real life operation. By simulating and accelerating the product aging, the HALT test reveals the product true reliability, and identifies time-related defects or design problems that may otherwise lie dormant for months or years. When the HALT test reveals faults in the tested product, design modifications are required and generally performed, followed by repetition of the HALT test, this time with the modified product. Such repeated tests and design modifications may occur several times, until satisfactory results are obtained.
Many types of laboratory tests are simulated using computer software. The performance of a computer simulation saves significant time and costs in comparison with a physical laboratory test, which requires expensive testing equipment, staff, and a significant amount of time for pre-test set-up, and for the test itself. In addition, obviously, a laboratory test requires a physical prototype, while a computer simulation is preferably carried out early in the design cycle, during the initial design process, and before a prototype is available. There are several typical procedures for performing such computer simulations. One of the most common procedures is the finite element technique, which can analyze the tested equipment behavior under various dynamic regimes of vibrations and thermal loads. The finite elements analysis technique can handle several dynamic regimes, including: (a) shocks in which the force or acceleration vary with time; (b) dynamic frequency or harmonic response where the model is analyzed in the frequency domain; and (c) dynamic random response where the model is subjected to a single-axis random vibration which is defined in terms of PSD. The term PSD stands for Power Spectral Density, or more particularly, to the power of random vibration intensity in mean-square acceleration per frequency unit (g2/Hz).
As said, the HALT laboratory test has been accepted in the art as one of the most reliable test for forecasting future failures. However, a simulation for a HALT test has not been provided yet. As noted, the HALT test applies simultaneous vibrations in six degrees of freedom, while all prior art finite elements solutions, including PSD finite element analysis, operate on a single axis dynamic regime at each given time. The art has not yet provided a simulation for a HALT test, or for other simultaneous-multi-axes loading tests for the purpose of forecasting failures in electronic or mechanical equipment.
It is therefore an object of the present invention to provide a simulation for reliability, robustness, or fatigue test, which can be performed without any need for physical testing facilities and without a need to have the physical tested object (i.e., the tested product itself).
It is another object of the present invention to provide a simulation for a HALT test, which can be performed without any need for physical testing facilities and without a need to have the physical tested object.
It is another object of the present invention to provide a simulation for a simultaneous multi axes loading test, which can be performed without any need for physical testing facilities and without a need to have the physical tested object.
It is another object of the present invention to provide a simulation for a reliability test designed to explore operational margins of a tested product, or to reveal the weakest components of the tested product, which can be performed without any need for physical testing facilities and without a need to have the physical tested object.
It is still an object of the present invention to provide such a simulation which can be performed as early as during an initial development stage of the product, for example, during the layout or initial design stages, or when a physical prototype of the tested product is not yet available.
It is another object of the present invention to save time and costs, by enabling the elimination of future failures at the early stages of the product development, and by eliminating or reducing the need of physical laboratory tests including HALT or any other laboratory test.
It is a particular object of the present invention to enable using the simulation for analyzing the reliability and robustness of the design of electronic boards and related equipment in the PCB industry.
Other objects and advantages of the present invention will become apparent as the description proceeds.